The present invention is concerned with improvements in air cylinder units and is more particularly related to improvements in control devices employed for controlling the extension and retraction of the piston and rod assembly of such units.
It is known to employ air powered cylinder units for various purpose, e.g., to use the extension operation of the unit rod and piston assembly to move or transfer an object along a conveyor on an assembly system or production line. In one such known type of unit, a control device of the type disclosed in U.S. Pat. No. 2,641,229 is used to control operation, i.e., unit piston rod and assembly extension and retraction by selectively positioning a slide member to admit pressurized fluid flow to either extend or retract such rod and piston assembly. In normal course of events operation, the said control device is well suited for its intended purpose. However, if a jam should occur on the line during the transfer operation so as to prevent the air cylinder rod and piston assembly from making its full extension stroke, the control device is not designed to prevent a potentially dangerous and undesirable operation condition. This potentially dangerous condition obtains during the extension operation because the control device piston and hence slide member are positioned or oriented for admitting air in the manner required to that end so that when an operator shuts down the air to the unit, clears the jam and reimposes air pressure to the unit, the control device piston positioning will remain the same and the rod and piston assembly will complete the previously interrupted extension operation before retraction operation can occur. If the operator has a hand in the way of the rod and piston assembly it could cause injury, or other transfer operational problems could ensue, e.g., damage to an article. Accordingly, it is desirable that such control device be designed such that upon release of air pressure from the unit as an incident attending clearing of a system jam, the control device automatically reorients its condition to effect rod and piston assembly retraction when air pressure is reimposed on the unit.